DOVER — State officials warn residents to become immunized as soon as possible against influenza and to arm themselves with pertinent information. The facts provided below came from the national Centers for Disease Control and Prevention and more information can be found by visiting their website www.cdc.gov.

What is influenza (also known as the flu)?

The flu is a contagious respiratory illness caused by influenza viruses that infect the nose, throat, and lungs. It can cause mild to severe illness, and at times can lead to death. The best way to prevent the flu is by getting a flu vaccine each year.

What are the signs and symptoms?

People who have the flu often feel some or all of the following — fever or feeling chills, though it important to note not everyone with the flu has a fever, sore throat, runny or stuffy nose, muscle or body aches, headaches, fatigue as well as vomiting and diarrhea in less common circumstances.

How long is a person with the flu contagious for?

You may be able to pass on the flu to someone else before you know you are sick, as well as while you are sick. Most healthy adults may be able to infect others beginning one day before symptoms develop and up to five to seven days after becoming sick. Some people, especially young children and people with weakened immune systems, might be able to infect others for an even longer period of time.

What flu vaccines are available?

The single best way to prevent the flu is to get a flu vaccine each season. The regular seasonal “flu shot” contains an inactivated vaccine with a killed virus. It is “intramuscular,” meaning it is injected into muscle, usually in the upper arm, and has been used for decades. A high-dose vaccine for people 65 and older which is also intramuscular is available, and was first created in 2010. The intradermal vaccine is for people 18 to 64 years of age and is injected with a needle into the skin, first created in 2011.

Additionally, there is a nasal-spray flu vaccine made with live, weakened flu viruses — sometimes called LAIV for “live attenuated influenza vaccine” — and is for people aged 2 to 49 years who are not pregnant.

About two weeks after vaccination, antibodies develop that protect against influenza virus infection. Flu vaccines will not protect against flu-like illnesses caused by non-influenza viruses. The seasonal flu vaccine protects against the three influenza viruses that research suggests will be most common. This year, those are Influenza A, B, and the H1N1 strain.